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Phylum Arthropoda > Subphylum Crustacea > Class Malacostraca > Order Decapoda > Anomurans > hermit crabs
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Introducing hermit crabs
updated Apr 2020

What are hermit crabs?
Have you ever eaten a crab? It's difficult to eat a crab, you have to crack open its shell to eat it.
Have you ever eaten a prawn?
A prawn has a long body is much easier to eat..

The front part of a hermit crab (its pincers and walking legs) have hard shells like a crab. But it has a long soft abdomen, like a prawn which doesn't have a shell. To protect its abdomen, it has to tuck it into an empty snail shell.

Hermit crabs belong to a group of animals called crustaceans. Other crustaceans include crabs, shrimps and prawns.

A closer look at hermit crabs

  • Look at the shells around you and see what is living inside it! Do this at a spot where there are likely to be many hermit crabs. "See, almost every empty shell has a hermit crab in it! That's why we should not take any shells home with us. Every empty shell is a potential hermit crab home. Even a tiny broken shell or an ugly shell covered with barnacles. One of the factors limiting the population of hermit crabs is the availability of suitable empty shells. So please don't take any shells away from our shores."

  • The hermit crab has many hitch-hiking friends! "What other animals can you see living with the hermit crab in its shell?"
  • A hermit crab home is a cosy and safe place for small animals.
    • Free airconditioning: the hermit crab keeps a constant flow of oxygenated water
    • Free left over food
    • Safe from predators and drying out: hermit crabs scurry into hiding places or bury themselves under sand.

  • Hermit crabs understood the concept of 'upgrading' long before other Singaporeans! As a hermit crab grows bigger, it has to find a bigger shell. Before switching shells, a hermit crab will tentatively test out the new shell first, while holding on to the old one. If the new one is not ideal, it instantly goes back into the old shell.

Hermit crabs are important to the ecosystem

  • Many animals live together with a hermit crab. If you remove a hermit crab, you also affect his many friends.

  • Many animals love to eat hermit crabs! They are an important part of the ecosystem. Can we think of some animals that might eat a hermit crab? Some charismatic animals to highlight: shorebirds, crabs.

  • Most hermit crabs are scavengers and eat up dead animals on the shore. They help quickly recycle dead things.

Hermit crabs and you

  • Should we keep hermit crabs as pets at home?
    • Hermit crabs sold as pets are usually taken from the wild.
    • Many die during the collection process, before they are even sold.
    • And many of those sold eventually die from neglect or ignorance of proper care.
    • Many small animals live with hermit crabs. Removing wild hermit crabs affects these small animals too.

Hermit crab myths to dispel

  • Hermit crabs belong in their shells! Please don't try to pull hermit crabs out of their shells. There are appendages at the end of the hermit crab's abdomen to hang on tight to the shell. If you pull the hermit crab, you may rip out their little appendages or tear their delicate abdomens.

  • A hermit crab does not necessarily always use the same kind of shell.

  • Hermit crabs never kill the original occupant of the shell. They may, however, quarrel with each other over a desirable shell.

Handling tips

Finding hermit crabs: Almost every shore will have some sort of hermit crab. A pile of small shells on a rock at low tide are usually inhabited by tiny hermit crabs. During the day, many are buried in the sand. Bigger ones may be found among seagrasses.

Be gentle! Do not poke or prod or shake hermit crabs to get them to come out.

How to get the hermit crab to come out?
The best way is to face the shell opening down and away from the light and wait patiently. Another harmless way to get them to come out is to pour plain water into the shell.

Remind visitors NOT to pull hermit crabs out of their shells. They will tear the animal in half as it has tiny claws on its butt to hang onto the shell.

Beware! Hermit crabs can pinch! Large hermit crabs can give a good pinch. Don't let small children handle them.
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